Public bug reported:
Environment
===========
Ubuntu 18.04.3 LTS
Linux 4.15.0-60-generic #67-Ubuntu SMP Thu Aug 22 16:55:30 UTC 2019 x86_64
x86_64 x86_64 GNU/Linux
libc6:amd64 2.27-3ubuntu1
gcc 4:7.4.0-1ubuntu2.3
Steps to reproduce the crash
============================
(note: all libraries are linked with --no-as-needed to keep them as
DT_NEEDED entries in the dynamic section, even though they are unused.)
1) create an empty library libNOTFOUND.so
2) create an empty library libB.so, linked to libNOTFOUND.so
3) create an empty library libA.so, linked to glibc's librt.so
4) create an empty library libPLUGIN.so, linked to libA.so and libB.so, set
DT_RUNPATH to '$ORIGIN'
5) create an empty library libMAIN.so
6) create an executable, linked to libMAIN.so and libdl.so, set DT_RUNPATH to
'$ORIGIN', this program calls:
a) dlopen("<absolute path to>/libPLUGIN.so")
b) dlopen("<absolute path to>/libMAIN.so")
Behaviour
=========
a) dlopen("<absolute path to>/libPLUGIN.so") fails because it cannot find
libNOTFOUND.so via default search methods. This is wanted and OK!
b) dlopen("<absolute path to>/libMAIN.so") raises SIGSEGV somewhere deep inside
the dynamic linking code of glibc (backtrace attached). Expected result:
returns a valid handle to libMAIN.so.
Comments
========
Attached is a simple test script which does all the steps from above and
also shows the workaround: Ensure that librt.so is loaded and fully
initialized before the failing call to dlopen("<...>/libPLUGIN.so")
happens. This can be done either via LD_PRELOAD or by linking the
executable to librt.so.
You can also replace librt.so with libpthread.so to reproduce this
behaviour. Any other library I tried instead of librt.so (e.g. libm.so)
does not trigger this bug.
I also attached a trace with LD_DEBUG=all. Here you can see that glibc
tries to relocate librt.so while it loads libMAIN.so. I would expect
that librt.so is loaded/relocated when libPLUGIN.so is dlopen'ed or that
it is neither loaded nor relocated because libPLUGIN.so has unmet
dependencies.
This example is a stripped down version of a real scenario where an
application was misconfigured.
** Affects: glibc (Ubuntu)
Importance: Undecided
Status: New
** Attachment added: "glibc-dl-test.sh"
https://bugs.launchpad.net/bugs/1842730/+attachment/5286782/+files/glibc-dl-test.sh
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https://bugs.launchpad.net/bugs/1842730
Title:
glibc: dlopen crash after a previously failed call to dlopen
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